1. Field of the Invention
This invention relates in general to improved shaped-charge devices and more specifically to an improved method for making a bimetallic shaped-charge liner of greater effectiveness.
2. Description of the Related Art
It is well known that the the penetrating power of an explosive charge can be enhanced by forming a cavity in the face of the charge. If the cavity is formed in a symmetrical manner about an axis, the cavity tends to direct the force of the explosion along the axis. A greater portion of the energy from the explosion can thus be directed in a specific direction at a specific target, such as for penetrating an armored vehicle. Although a wide variety of cavity configurations is available, a conical or a cup-shaped cavity is most commonly used.
The effectiveness of a shaped-charge is further enhanced by lining the cavity with an inert material such as, for example, metal or glass. Upon detonation of the explosive charge, a high velocity pencil-like jet with high kinetic energy is formed from the liner material and is projected along the axis of the liner. Because of its high velocity and high kinetic energy, this jet is capable of penetrating solid material. In munition applications, the shaped-charged device is thus used to destroy armored vehicles by penetration of the protective armor. A liner is generally formed of a dense, ductile material, such as copper, which has been shown to have good penetrating ability.
While high density metals, such as copper, are excellent penetrators, they have little or no capability for beyond-armor effect, so that a follow-through charge is often employed to increase the lethality of the munition.
One concept featuring this enhancement of lethality is the use of pyrophoric metals for incendiary effects either as a liner or in a position for following the jet. This typically means the use of aluminum, magnesium, and other less dense metals.
The pyrophoric metals proved unsatisfactory as liners because of their poor penetration ability, so consequently, it was proposed to use a double-layer liner having a precursor cone of dense metal, for its penetration ability, and a follow-through cone of light metal for its incendiary effects. However, tests have shown that any gap between the metal liners greatly reduces the effectiveness of the jet. A gap, even as thin as an oil film between the metals, appears to produce a dis-continuous jet of greatly reduced penetrability. Tests indicated that a metal-to-metal interface was necessary for a continuous, high-penetration jet. The object of the research then became to create a bimetallic cone with no discrete interface between the metals.
Many approaches to solving the interface problem were tried and were found to have disadvantages. Some of these disadvantages were particularly related to the specific function of creating a penetrating jet.
To produce the desired liner, the precision machining of two perfectly mating cones was considered. Precision machining has several drawbacks. It is extremely expensive and time consuming. Additionally, even with the most precise machining, it is difficult to avoid all interface gaps and difficult to avoid inclusion of contaminants which degrade the interface. Another concept was to shear-form the two metals simultaneously over the same mandrel, thereby producing a conical liner of two metals. However, because of the differences in the flow characteristics of the different metals and inadequate shear force propagation, separation of the liners occurs during the process. Producing the bimetallic liner by metal deposition is prohibitively expensive and time consuming. Diffusion bonding or brazing two similar metal cones generally produces an intermediate surface containing intermetallic compounds that are brittle and greatly diminish the effectiveness of a jet.
The idea then surfaced that, if the two metals could be physically joined with a strong enough bond to resist the shearing forces that cause separation during shear-forming, then it may still be possible to shear-form the two metals simultaneously. Several conventional methods, including brazing and diffusion bonding, to pre-bond the metal prior to shear-forming, were attempted. These methods are relatively expensive and time consuming. In addition, the heat treatment used in these processes creates a brittle intermetallic interface which cannot be easily removed. This brittle interface material prevents controlled liner collapse and jet formation.
Therefore, it is desirable to have a method of producing a functional bimetallic, shaped-charged liner. It is further desirable that the method of manufacture be economical.